Fourastronauts working to swap control of the International Space Station (ISS)between their two crews said Thursday that the process is going smoothly as they hit themidpoint of their work together.

Afternearly six months of spaceflight, Expedition11 commander Sergei Krikalev and flight engineer John Phillips are now intheir fourth day of handover operations with the station's new crew - Expedition12 commander Bill McArthur and flight engineer Valery Tokarev.

"There areno serious problems," Tokarev told SPACE.com from orbit via a communications link, adding that the spacestation is in good condition. "Sergei and John worked really hard and did a lotof work to maintain the station."

Tokarev andMcArthur arrivedat the ISS on Oct. 3 with U.S. space tourist GregoryOlsen, and will spend about eight days preparing to take the station's reins.Krikalev and Phillips will return to Earth with Olsen on Oct. 10, though itwill be early Oct. 11 local time in Russia when their Soyuz TMA-6 space capsuletouches down.

Olsen ispaying $20 million for his 10-day spaceflight, during which he will spend aweek aboard the ISS. He is the third fare-paying visitor to the space stationand is conducting three medical experimentsfor the European Space Agency, as well as Earth observation.

"It's goingto be a facility that's going to serve science for many years to come,"Phillips said of the space station.

As part oftheir joint activities, Phillips and McArthur worked earlier today to prepare partof the station's new Human Research Facility rack - which arrivedaboard the space shuttle Discovery in July - for full science operations.

"I got toroll up my sleeves just a little bit today," McArthur said of that work, addingthat he looks forward to using the new research station.

Every bitof new science hardware and space station construction is vital to human explorationof space, Krikalev said.

"Our [space]station construction is the biggest technical experiment...where we learn how tobuild the space station and how to create something different," Krikalev said. "Ithink this experiment is still going, and going well."